At the end of January 1968, the North Vietnamese and Vietcong forces launched surprise attacks in cities and villages across South Vietnam just as the country was starting to celebrate Tet, the Vietnamese lunar new year. After being caught off guard, U.S. and South Vietnamese forces repulsed the attacks and inflicted heavy losses. Although the Tet Offensive proved to be a failure on the battlefield for the Vietcong, it helped turn public opinion in the United States against the war and persuaded President Lyndon Johnson not to run for reelection.

James M. Lindsay, CFR’s senior vice president and director of studies, says the Tet Offensive demonstrates a cardinal rule of politics: never overpromise and under-deliver. The Johnson administration had said prior to the 1968 offensive that the war effort was making progress. Tet created a "credibility gap" once the public saw that the war wasn’t headed for a quick end. Preparing the public for potential reversals and setbacks is critical to fashioning any foreign policy that requires a sustained political commitment, Lindsay says, and a point worth remembering as talk in the United States turns to a potential military strike at Iran or possible intervention in Syria.

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